Mercury cathode discharge tube



June 20, 1939. H. LEMs Er AL MERCURY CATHODE DISCHARGE TUBE Filed June 26, 1957 Patented June 20, 1939 MERCURY CATHODE DISCHARGE TUBE Hendrik Lems and yCornelis Bastiaan Los, Eindhoven, Netherlands, assignors to N. V. Philips Gloeilampenfabrieken, lands Eindhoven, Nether- Application vJune 26, 1937, Serial No, 150,623 YIn Germany Julyv 6, 1936 7 Claims.

Our invention relates to mercury-cathode discharge tubes and more particularly to cathodespot anchoring bodies for such tubes.

Usually such bodies are made of a metal whose 5 surface is capable of being wetted bythe cathode mercury, either by amalgamation or due "to its cleanliness. rIf the bodies are made-of an oxidizable metal, such as nickel, it is necessary-to completely remove by reduction the oxide layer Vwhich is always formed during the manufactureof'the tube, in order to allow the amalgamation. On the other hand, if the bodies are madefo'fa metal fwhich oxidizes with diliiculty, i. e. metals Awhich remain vclean and lretain their anchoring vproperties under all*4 conditions and even lat high temperatures, it is necessary touse one of the noble metals, which are comparatively expensive. -Although it is possible to use onlyfa layer of av noble metal and a core of a cheap metal suchas copper, `in such cases the layer must be relatively thick in order that it will not be destroyed within a-short ftime by the discharge and Vuncoverjthe corelmaterial which is not adapted to 'anchor the cathode spot. This latter construction, in addition to being expensive, also lentails manufacturing ldifilculties. Y Y Y v The'object of our invention is to overcome the above difficulties and 'to provide 'an anchoring spot body which is inexpensive 'and atvthe same time meets all operating conditions. A

In accordance lwith the invention, we form the 4composite vanchoring member from a substratum of a metal Which has satisfactory vanchoring properties Abut which readily oxidizes Yat high temperatures, and provide this substraturngprior to the assembling of the tube, with 'a thin coveri- 'ing'or protective layer of a metal which also has satisfactory anchoring properties b'ut'which does not oxidize at high temperatures.

4'0 More particularly, in one embodiment of our invention we use a core of nickel andjproyide -same witha protective layer 'of platinum having `athickness of Vseveral microns.

The protective orcovering layer need have a thickness 'of only a few'microns becausegitis .not intended to remain 'int'act during even normal operation of the finished tube, Aas the Vcore when uncovered cannot oxidize in the vacuum of the tube and its surfacehas satisfactoryanchoring properties. Thusthe anchor-ing body remains free from oxide 'during the manufacture of the tube, and after the tube is completed, the loss of the covering layer can no longer affect the anchoring properties of the anchoring body.

55 n In another embodiment of our invention, which body raccording to another embodiment of the invention.

`anode 9.

(Cl. Z50-27.5)

cathode rectifier embodying the invention;

Fig. 2 is a lsectionized view of an anchoring l5 body according to one embodiment of the 4invention; and 'v Y Y y Fig.c3 is Y'a sectionized View of an anchoring 20 Y The'rectier shown in Figure 1 has an Yenvelope comprising a 'cup-shaped metal member I, for injstance `of chrome iron, and a glass member 2 hermetically fused together at II.

Disposed in the bottomo'f member I is a mercury'cathode 3, 25 whereas a 'main anode V8 is supported from the lower endoi a conductor 6 whose rupper'end is `secured to a metal disc 4 hermetically sealed in glass portion 2 and carrying a suitable terminal. Supported from conductor 6 and surrounding 30 anode is la cylindrical screen II serving to protect the higher internal surfaces of portion I and Y'seal "I1 from the detrimental effects of the discharge.

Supported by screen II, which is preferablyof rod I9 carrying on its lower end an auxiliary The anode 9 is adapted to'be moved in the direction ofthe double-headed arrow, and 40 for this purpose the upper end of rod I9 carries a `plunger 'I8 of magnetic material electrically connected through a compression spring 22 'Ito a core 2I of amagnetic material. `Core 2| is supported from the lower end oi a Vconductive '45 rod'l secured to a disc 5 hermetically sealed in glass portion 2. Outside the envelope and surrounding core 2| vis coil I0 whichfserves to raise anode 9 from the surface of the-mercury.

Surrounding the metal member `I is. a cooling ljacket I2 'having an inlet opening I3 and an outlet opening I4, and through whichv al circulating cooling medium, such as water, is circulated in the direction of the arrows during operation of the rectifier. Jacket I3 is secured to metal 55 member I by a copper bolt .I5 secured, for instance by welding, to the bottom of member I and serving to supply current to cathode 3.

Secured to the upper surface of the bottom of member I is an anchoring body 26, later to be discussed.

Within the bottom of member I and extending slightly from the surface of mercury 3 is an annular member 25, for instance of molybdenum,

which serves to prevent the cathode spot from, disengaging from body 26, for example, due to excessive loads, and reaching the inner wall of member I over the surface of mercury 3. For normal loads, however, the cathode spot will form on the line of contact between the mercury cathode 3 and body 26, a line-shaped area of application whose length is proportional to the discharge current.

In accordance with the invention and as is indicated in Figure 2, the anchoring body 26 is formed of a core 2l of a metal of good anchoring properties but which readily oxidizes, and a thinprotective layer 28 of a material oi good anchoring properties and which does not oxidize. The core 2l may be of a metal such as nickel, or molybdenum, whereas the layer 28 may be'of a metal such as platinum, iridium, palladium, or rhodium. As the layer 28 does not serve any function during the operation of the tube, it may be very thin, for instance of the order of a few microns. For example in the case of platinum it may be about 5 microns.

In constructing the tube, core 22 is secured to member I, for instance by welding or soldering, and the layer 28 is then applied by the wellknown electroplating process or by cathode disintegration. Y,

We prefer to make the anchoring body of a nickel core coated with a platinum layer because nickel has the advantage that itV amalgamates with mercury when it has a clean surface, and on the other hand is attacked by the mercury and the cathode spot at such a low speed that a completely satisfactory life of the anchoring body and thus of the tube can be obtained.

Because of this low speed of attackv it is possible to further reduce manufacturing costs by making the core of any convenient metal, and a thick layer of an oxidizable metal of good anchoring properties which is covered with a thin covering layer of non-oxidizable metal of good anchoring properties.

Such a construction is illustrated by the anchoring body of Figure 3, which comprises ar core 29, a layer 30 of the same material as core 21 of Figure 1, and a covering or protective layer 28.

Core 29 is made of an inexpensive metal which can be worked in a satisfactory and simple manner, for instance by drawing or pressing. For this purpose metals such as copper, or aluminium, or alloys having a high percentage of copper may be used; however we prefer to use copper because it has a high heat conductivity. This allows a maximum heat dissipation from the active surface of the anchoring body through the body to the artificial cooling liquid, to thereby maintain the active surface at the proper temperature, essential for satisfactory functioning of the anchoring body.

The thickness of layer 30 depends upon the material used, and in the case of nickel we have found that a thickness of about 2 mm. gives a sufciently long life of the anchoring member. Greater thicknesses may even be inadvisable since, particularly when a copper core is used, dissipation of heat is unnecessarily reduced by the poorer heat conductivity of the thicker nickel layer. Y

- While we have described our invention in connection with speciiic examples and applications,

Vwe do not wish to be limited thereto, but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What We claim is:

1.` A dischargeV tube comprising an envelop, an anode, a mercury'cathode, and a cathode-spot anchoring body, said body comprising a nickel substratum, and a thin protective layer of platinum. f

2. A discharge tube comprising an envelope, an anode, a mercury cathode, and a cathode-spot anchoring body, said body comprising arcore of an inexpensive metal, alayer of nickel upon said core and adapted to act as the final anchoring body, and a thin protective layer of platinum upon said nickel layer.

V3. A discharge tube comprising an envelope, an anode, a mercury cathode, and a cathode-spot anchoring body, said body comprising a core `oi. an inexpensive metal, a layer of. nickel upon said core and having a thickness of about 2 mm., and a thin protective layer of platinum upon said nickel layer. Y v

4.` A discharge tube comprising an envelope, an anode, a mercury cathode, and a cathode-spot anchoring body, said body comprising a copper core, a layer .ofl nickel upon said core, and a thin protective layer of A`platinum upon said nickel layer and having a thickness of the order of a few microns. Y Y l 5. A discharge tube comprising an ,envelope having a metal portion, an anode, a mercury cathode Within said metal portion, and a cathode-spot anchoring body secured to said metal portionLsaid body: comprising a core of an inexpensive metalof highrheat conductivity and having one surface secured to said metal -portion, a layer` of nickel covering the remaining surfaces ,lofsaid core, and a thin protective layer of platinum upon said nickel layer. j v

6. In'a ymercur'y-cathofde' discharge Itubeja cathode-spot anchoring member comprising a substratum of a readily-.oxidizable metal of good anchoring properties selected from the group consisting of nickel and molybdenum, and a` thin protective layer of a non-oxidizableand mercuryresistant. metal of good anchoring properties selected from the group consisting of platinum, iridium, palladium and rhodium.

"7. In a mercury-cathode discharge tube, a cathode-spot anchoring member comprising a substratum of a readily-oxidizable metal of good anchoring properties selected from the group consisting of nickel and molybdenum, and a thin protective layer of a non-oxidizable and mercuryresistant metal of good anchoring properties se-I lected from the groupconsisting of platinum,

iridium, palladium'andrhodium, said layer lhaving a thickness' of` the order of several microns.

HENDRIK LEMs. ooi-minasy BAs'rIAAN Los. 

